The most important hydrocarbon refining process, which in the 1940's revolutionized the refining industry, is catalytic cracking of large hydrocarbon molecules. The catalytic cracking process is the largest catalytic process in the world, and is extensively used today for the production of gasoline from high boiling hydrocarbons such as residual and gas oil fractions. In many refineries heavy residual oil resulting from distillation of crude oil, or so called topped crude or simply resid, is pretreated in a hydrotreating process before sending the resid to a fluid catalytic cracking (FCC) process step. As used herein a "heavy oil" is taken to mean a hydrocarbon liquid boiling at atmospheric pressure in a range of from about 650.degree. F. to as high as 1500.degree. F., and which contains a variety of very complex chemical compounds.
A principal factor which affects the economic viability of a fluidic catalytic cracking unit is the amount of the feedstock that is converted to a desired product such as gasoline. In many refineries the feed to an FCC unit consists of a heavy oil containing an unlimited mixture of complex molecules of straight and branched paraffins, cycloparaffins, and aromatics ranging from monoaromatics to four or five rings with a vast variety of side chains. It is generally very difficult to maintain a desired conversion of this heavy oil feedstock in an FCC unit.
In recent years the use of computers has increased greatly as a means to examine complex chemical reactions by simulation techniques. Digital computer simulation of catalytic cracking reactions is particularly valuable in many areas relating to refining of heavy oil such as predicting what a cracking reaction will yield under different operating conditions, in optimizing operation of a riser reactor, in planning and scheduling operations, and perhaps most importantly in selecting optimum crude and catalyst purchases.
An effective kinetic model to describe riser reactor cracking of hydrocarbon oils includes two essential features: First is a reasonable physical description of the riser reactor dynamics, accounting for variations in temperature, space velocity, residence time, cracking rates and catalyst deactivation over a wide range of feed stock composition and process conditions. Second is reliable predictions of the variation of the rate constants for cracking and product selectivity as a function of oil and catalyst properties.
A highly effective method and apparatus for simulating a catalytic cracking reaction by relating conversion, selectivity, and product yields to feedstock properties is disclosed and claimed in U.S. Pat. No. 5, 774,381 issued Jun. 30, 1998, to Paul F. Meier. However, the method disclosed in that patent relates hydrocarbon conversion to process variables and to feedstock properties that are routinely measured at the refinery such as API gravity, measured impurities (sulfur, Ni, and V), basic nitrogen, carbon residue and viscosity. While the disclosure of this patent is regarded as representing a significant contribution to the simulation art in predicting conversion of heavy hydrocarbons to cracked products, it is insufficient to differentiate chemical differences between crude feed types, i.e., sweet or sour, or between pretreatment, i.e., virgin or hydrotreated, or between fresh or recycle streams. Accordingly, it would be highly desirable to have a kinetic model for a riser reactor in catalytic cracking that is independent of the feed source or pretreatment.
An object of this invention is to improve efficiency of commercial refining operations.
A more specific object is to predict how well a specific oil fraction would run in a riser reactor of an FCC Unit.
Another object of this invention is to obtain data that facilitates improved selection of catalyst and/or crude oil stocks purchased for processing in a refinery.
Yet another object is to obtain kinetic reaction data that can be integrated into a process model for optimized operation of a total FCC process.
Still, another object of this invention is to make the kinetic model independent of the feed source and pretreatment.
Another more specific object of this invention is to predict essentially continuous boiling point distribution curves of C.sub.5 cracked hydrocarbon products.